JPH01184033A - Production of cubic boron nitride - Google Patents

Abstract

PURPOSE:To efficiently produce cubic boron nitride by treating pyrolytic boron nitride in which a hexagon scaly hexagonal boron nitride particle is random- oriented and the interlaminar distance of the c-axial direction is regulated to a specified range under high temp. and high pressure without using a catalyst. CONSTITUTION:Pyrolytic boron nitride (BN) having such a structure that a hexagon scaly hexagonal boron nitride (hBN) particle is random orientated in a state intactly deposited from a vapor phase and having interlaminor distance (d 002) of the c-axial direction not larger than 3.35Angstrom , density not smaller than 2.18g/cm<3>, size of a crystalline particle of the c-axial direction not smaller than 100Angstrom and 99.995% purity is synthesized. Cubic boron nitride (cBN) is produced by treating this pyrolytic BN at the temp. not lower than 1,500 deg.C at the pressure not lower than 0.05 million atm. without using a catalyst. This cBN is utilized as the heat sink of an electron device.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for producing cubic boron nitride (CON) by a non-catalytic direct conversion method, and in particular to a method for producing cubic boron nitride (CON) using pyrolytic boron nitride (CON) as the raw material low-pressure phase boron nitride. The present invention relates to a method using P-BN).

(Prior art) CBN, which is a high-pressure phase of boron nitride, has hardness and thermal conductivity second only to diamond, and is chemically stable, so it is used as tools for machining ferrous metals and semiconductor devices. Its use as a heat dissipation substrate is progressing.

CBN is usually obtained by treating hexagonal BN (hBN) or turbostratic BN (tllN), which is a low-pressure phase of boron nitride (BN), at high pressure and high temperature. , 50,000 atm, 2100℃
Because the above-mentioned very severe conditions are required, industrially, catalysts are used to make the conversion conditions relatively mild, such as 40,000 to 50,000 atm and about 1,500°C. By this method, single-crystal CBN particles are produced and are used as they are as abrasive grains for grinding tools such as whetstones. Additionally, a sintered body for cutting tools can be obtained by sintering fine CBN particles under high pressure and high temperature, but since CBN is difficult to sinter by itself, it is mixed with a bonding agent such as metal or ceramics before sintering. There is a need. CBN currently used industrially
Most of them are manufactured by the above-mentioned method, but there is a problem that the incorporation of catalyst and the presence of a binding aid for sintering deteriorate the inherent properties of CBN, and therefore, CBN is manufactured without using a catalyst or a sintering aid. Non-catalytic direct conversion method (hereinafter referred to as direct method)
Therefore, it is desired to realize the production of CBH particles and sintered bodies under milder conditions. C, BN produced by the direct method is a polycrystalline substance composed of fine particles, and is expected to have characteristics such as high hardness, high purity, high thermal conductivity, and high toughness, and exhibits excellent properties as a tool material and a heat dissipation substrate. It is expected that

The following literature has been published as a method for producing CBN by a direct method that has been reported so far.

Literature i) Wakatsuki et al.: “Synthesis of Polycrystalline Cubic Boron Nitride”, “Materials Research
Research Bulletin) J, 7
．． 999~Reference ii) Ichise et al.: “Synthesis op Polycrystalline Cubic Boron Nitride (V)”, rProsedinges Op Force.
International Conference of High Pressure (Proceedings of 4thIn
International Conference on
lligh Pressure) 4436-440
(1974) Document iii) Corrigan, JP-A-54-33510 Document i, 125
Temperatures above 0°C and 60kbar (approximately 60,000 atmospheres)
By processing at higher pressures, "lump"
It has been reported that J-shaped CBN was obtained. However, in this example, it has been pointed out that 120 may have acted as a catalyst (Osamu Fukunaga, "Synthesis and Applications of Cubic Boron Nitride").

Ceramic Data Book “85.431-436 (
(1985)), there are no follow-up examples, and there are many unclear points.

In document ii, pyrolytic boron nitride (PBN or P-
(abbreviated as BN) as a starting material and 1800 to 1900
Direct conversion at a temperature of 69 kbar (about 69,000 atm) has been attempted;
Conversion to BN has not been achieved.

Document III reports that a CBN sintered body can be obtained by subjecting a P-BN compact to high-temperature, high-pressure treatment at a temperature of 1800° C. or higher and a pressure of 50 kbar or higher. In addition to the above, there are several reports on methods for producing CBN without using catalysts, but all of them involve high-temperature, high-pressure treatment under severe conditions, such as temperatures of 1800°C or higher or pressures of 60 kbar or higher. By C
This is a method for producing BN, and is unsuitable for industrial production.

On the other hand, the method of the above-mentioned document ii uses P-BN as a raw material. P-BN is low-pressure phase boron nitride manufactured by chemical vapor deposition (CVD), and is commercially available in the form of a crucible or a plate. Conventional P-BN is not a perfect hexagonal crystal, but has a so-called turbostratic structure, the distance between the eyebrows in the C-axis direction is wider than hBN (about 3.40 people), and the density is about 2. lO~2.18 g/cm
3. Crystallite size is 50-100, purity is 99.9
It is 9% or more (this is called U-PBN in Document II). In addition, as for other conventional P-BN, the above-mentioned 1l-PBN was prepared in accordance with the method disclosed in U.S. Pat.
The glabellar distance in the C-axis direction obtained by hot compression at a temperature of 50°C or higher and a pressure of 5000 psi (340 atmospheres) or higher is 3.33 people, and the density is 2.28 g/cm.
”, there is P-BN with a purity of 99.99% or higher (this is called R-PBN in Literature City). In Literature ii, similar to Literature ii, there is P-BN with a purity of 99.99% or more. −
PBN and R-PBN) are directly treated at high temperature and high pressure to
When producing a BN sintered body, this P-BN contains almost no impurities that inhibit sintering, making it a strong CBN.
It is stated that a sintered body can be manufactured, and the high temperature and high pressure treatment conditions in this case are in the claims.
℃ or more and a pressure of 50 kbar (approximately 50,000 atmospheres) or more, but according to the detailed description of the invention, it is said to be a temperature of about 1800 °C to 2000 °C or more and a pressure of 60 kbar or more. . Also, according to the description in Examples, the temperature is 1580°C.

At 65 kbar (approximately 65,000 atm), no conversion of CBN occurred even after treatment for 30 minutes (Example 4. Test 4A)
, severe high-temperature and high-pressure processing conditions of 2100° C. or higher and 65 kbar or higher are required. Therefore, the method of document iii is unsuitable for industrial production.

(Problems to be Solved by the Invention) The purpose of the present invention is to make it possible to synthesize CBN by a direct conversion method under conditions of lower temperature and lower pressure than the conventional method. The purpose of the present invention is to efficiently produce high-purity CON that has not been purified, and to obtain CBN particles or sintered bodies thereof that exhibit the original characteristics of CBN.

(Means for Solving the Problems) The present inventors have developed a method for producing CBH using a non-catalytic direct conversion method, in particular the synthesis of P-BN used as a raw material, that is, hexagonal boron nitride, which is low-pressure phase boron nitride. As a result of studying the relationship between the method, the characteristics of this raw material, and the conversion conditions of CBN, we found that even after post-treatment such as hot compression, the crystallinity is extremely high and the crystal structure of hexagonal boron nitride is almost perfect. In addition to discovering a technology to synthesize high-purity boron nitride using the CVD method, we also discovered that by using this as a raw material, it was possible to convert it to CBN under conditions of higher temperature and higher pressure that were milder than before. This is what we have come to.

P-BN, which is the low-pressure phase boron nitride used as a raw material in the present invention, is synthesized by the CVD method, but unlike P-BN, which is the conventional CVD method BN, it has hexagonal scale-like fine particles unique to hexagonal BN. It has a randomly oriented microstructure, and the glabellar distance in the C-axis direction is 3.35 Å or less in the CvD state without being subjected to hot compression treatment like R-PBN. , density is 2.18
g/am3 and the crystallite size in the C-axis direction is 1
000 Å or more and has a purity of 99.995% or more.

(Function) Conventional P-BN consists of a continuous film of oriented low-pressure phase boron nitride produced by the CVD method, and is commercially available as a laminated plate with a thickness of about a few inches. The production of P-BN by the CVD method is described, for example, in U.S. Patent No. 3.152.
As disclosed in the specification of No. 006, boron halide gas such as boron trichloride (BCl s) and ammonia gas are used as raw materials, and 1
It is carried out by depositing low-pressure phase boron nitride from the gas phase on the surface of a substrate such as graphite at a temperature of 400 to 2300°C. As described in literature iii, the characteristics of conventional P-BN include a purity of 99.990%, a density of 2.10 to 2.18 g/cm3, and a preferential orientation in the C-axis direction. It was found to be highly oriented at an angle of 50 to 100 degrees, and to have a turbostratic crystal structure with low crystallinity.

On the other hand, P-BN used in the present invention has a pressure of 2T, for example.
orr or less, temperature 1950'C or more, deposition rate 100
It is produced by spraying BCf3 and N113 gases, which are raw materials, onto the substrate at a high flow rate, specifically, as a jet flow of 100 m7 seconds or more, at a flow rate of 100 m7 seconds or less. Compared to conventional P-BN manufacturing conditions, these conditions are characterized by high temperature and low deposition rate, and in that the raw material gas is blown in a jet shape.

If even one of these conditions is not met, that is, if the temperature is too low, the deposition rate is too fast, or the raw material gas flow rate is too slow, highly crystalline BN that can be used as a raw material in the method of the present invention is not obtained, and the conventional P-BN
In other words, BNL with a turbostratic structure and an oriented structure cannot be obtained. In general, P-BN differs from normal hBN in that the raw material for production is gas, and thus high purity can be easily obtained by increasing the purity of the raw material gas.

Conventional P-BN is, for example, 99.99% for the reasons mentioned above.
Although the purity was as high as above, the interlayer distance in the C-axis direction was 3.
The crystallinity was large, more than 40 Å, and low. Meanwhile, according to the method disclosed in U.S. Pat. No. 3,578,403, conventional P-BN was heated at 2250°C under an inert atmosphere.
Highly crystalline P-ON' can be obtained by hot compression at temperatures above 5,000 psi (340 atm) and above.
However, in this method, the heat treatment temperature is 2250°C.
This is high, and since P-BN is in contact with graphite, which is a pressure medium, P-BN decomposes to produce boron, and impurities such as carbon from graphite are mixed in. Therefore, the purity of the generated P-BN decreases.

P-BN (R-PBN) subjected to such treatment is highly oriented, has a high selective orientation of 2 to 0 degrees in the C-axis direction, and has a microstructure of a laminated structure.

Such conventional P-BNs (U-PBN and R-PB
In contrast to N), P-BN, which is the raw material for the method of the present invention produced under the conditions described above, has a microstructure that is not an oriented layered structure, but has almost completely hexagonal scale-like particles of hexagonal BH. It has a randomly oriented structure, and the orientation is 10 in the C-axis direction.
It is more than 0° and hardly recognized, and its crystallinity is C
Even in the state where it was opened, it was already high (the interlayer distance in the C-axis direction was 3.35 Å or less, and the density was 2.18 g/C
m3, and the crystallite size in the C-axis direction is 10
00 Å or more, does not contain free boron or carbon, and has a purity of 99.995% or more, which is high purity. The above points are the differences between P-BN, which is the raw material for the method of the present invention, and conventional P-BN.

When producing CBN without using a catalyst using raw materials different from those of the present invention, for example, as in the examples of the literature pile, temperatures of over 2100°C and pressures of over 65 kbar may be used. Although high-temperature and high-pressure treatment under severe conditions is necessary and is not suitable for industrial production, when the raw material of the present invention method is used, temperature and pressure conditions with excellent productivity such as 1500 to 2100°C and 50,000 to 60,000 atmospheres can be achieved. This makes it possible to produce CBN without using a catalyst.

The reason why direct conversion to CBN is possible even under such mild conditions is believed to be as follows.

First, a major difference between conventional P-BN and P-BN, which is the raw material of the present invention, is the presence or absence of structural anisotropy.

The conversion from low-pressure phase BN to CBN is caused by the large-gonal crystal form B of the low-pressure phase.
This is thought to occur when B and N atoms, which are arranged in the (001) plane of N to form a hexagonal net plane, shift out of the plane in opposite directions, and here the low-pressure phase B of the raw material
When N is oriented, even if pressure is applied hydrostatically, only the pressure component perpendicular to the oriented plane will effectively act on the conversion.

On the other hand, since P-BN, which is the raw material of the present invention, has no orientation, the pressure component can be used effectively, and this is thought to be one of the reasons why the conversion conditions are mild. Next, if the low-pressure phase boron nitride that is the raw material has low crystallinity (U
In order to convert the low-pressure phase boron nitride into CON (-PBN), severe high-temperature and high-pressure treatment conditions are required.
It is thought that the state changes to N and then to CBN, and this first stage change to a highly crystalline state requires an extremely large amount of energy. In addition, when the raw material low-pressure phase boron nitride has low purity (R-PBN), impurity atoms present here and there in the crystal lattice are boron atoms and nitrogen atoms when the low-pressure phase boron nitride is converted to CBN. It is thought that it acts as an obstacle that prevents the movement of atoms, and therefore requires severe high-temperature, high-pressure treatment conditions.

P-BN, which is a raw material for the method of the present invention, is processed into a disk or powder and filled into a belt-type high-temperature and high-pressure generator. Thereafter, the pressure is first increased, then the temperature is increased, and the required temperature and pressure are maintained for a certain period of time to perform high-temperature and high-pressure treatment. At this time, the holding temperature, pressure and time are preferably 1500 to 2100°C, 150,000 to 60,000 atm, and 30,000 atm, respectively.
It is 0 minutes to 2 hours. After the treatment, first the temperature and then the pressure are returned to room temperature and 1 atm, respectively, and the CON produced by the high temperature and high pressure treatment is taken out from the apparatus. The resulting CBN is CBN produced without the use of conventional catalysts.
Manufactured under milder temperature and pressure conditions than

In this way, the present invention was able to achieve a highly productive manufacturing method that produces CBN with excellent properties.

(Example) Next, the present invention will be explained with reference to examples.

99.999% purity BCj! +Gas and purity 99.99
The mixed gas with 9% annimore gas was heated to a pressure of 2 Torr.
A BN film with a thickness of 1.1 mm was obtained by spraying onto a graphite substrate at a gas flow rate of 200 m7 seconds under conditions of a temperature of 1950° C. and a deposition rate of 80 μm/hr. When this BN film was released from the base material and observed under an electron microscope, it was found that it had a structure in which hexagonal scale-shaped particles of about several μm in size were randomly oriented. The interlayer distance in the C-axis direction and the crystallite size in the C-axis direction of the produced BN were measured by X-ray diffraction and were found to be 3.34 Å and 1000 Å or more, respectively. The preferred orientation in the C-axis direction was 120°. Result of density measured by Archimedes method: 2.20
g/cm 3 , and the purity was determined by chemical analysis to be 99.998%. The produced BN film was processed into a disk and used as a raw material, and subjected to high temperature and high pressure treatment for 1 hour under the temperature and pressure conditions shown in Table 1 using a belt type high temperature and high pressure generator. All of the products were strong sintered bodies in which C88 particles were densely aggregated, and as a result of X-ray diffraction measurement, no crystal phase other than CON was identified.

This [L2] The interlayer distance in the C-axis direction and the crystallite size in the C-axis direction of a commercially available P-BN molded body were measured by X-ray diffraction, and the results were 3.42 and 80, respectively. The density was measured by Archimedes method and was 2.12 g/am', and the purity was measured by chemical analysis and found to be 99.990%.

Further, when observed using an electron microscope, it was found that the P-BN plate had a laminated structure in which planes perpendicular to the thickness direction were stacked. This P-BN molded body was processed into a disk and used as a raw material, and was heated under high temperature and high pressure for 1 hour under the same temperature and pressure conditions as in Examples 1 to 12 using a belt type high temperature and high pressure generator as shown in Table 1. processed. Depending on the temperature and pressure conditions, the products can vary depending on the temperature and pressure conditions, as shown in Table 1.
They were in various forms such as N sintered bodies.

Implementation Team Leader The same P-BN as in Examples 1 to 12 was processed into a disk and used as a raw material, and using a belt type high temperature and high pressure generator,
High temperature and high pressure treatment was performed for 30 minutes under the temperature and pressure conditions of C and 54,000 atm. The product is a strong sintered body of densely aggregated C88 particles, with a density of 3.48 g/Cl
113, and no crystal phase other than CBN was identified. The thermal conductivity of the 2000N sintered body at room temperature was measured using a steady thermal conductivity measuring device (manufactured by Rigaku Denki, TS-Lλ8550).
The result was 9.5 ni/Clll-.

Implementation U The same P-BN as in Examples 1 to 12 was processed into a disk and used as a raw material, and heated to 1700°C using a belt type high temperature and high pressure generator.
Then, high temperature and high pressure treatment was performed for 2 hours at a temperature and pressure condition of 55,000 atm. The product is a strong sintered body of densely aggregated C88 particles, with a density of 3.46 g/cut'
Therefore, no crystal phase other than CBN was identified. When we measured the micro Knoop hardness of this CBN, it was found to be 3500k.
g/mm".

Implementation ■DanjiU The same P-BN as in Examples 1 to 12 was pulverized to obtain powders having the average particle diameter shown in Table 2. This was subjected to high-temperature and high-pressure treatment using a belt-type high-temperature and high-pressure generator under the conditions shown in Table 2, and as a result, a CBN mass was formed. This CBN mass was easily ground into C88 particles having the average particle size shown in Table 2. As a result of measuring this C88 particle by X-ray diffraction, no crystal phase other than CBN was identified.

Further, when the microstructure of the C88 particles was observed using an electron microscope, it was found that the C88 particles had an irregular shape and were polycrystalline.

Comparative Plate U2 The same P-BN as in Comparative Examples 1 to 12 was pulverized to obtain powder having the average particle size shown in Table 2. This was subjected to high-temperature and high-pressure treatment using a belt-type high-temperature and high-pressure generator under the conditions shown in Table 2. As a result, the product was a brittle solid. As a result of measuring this product by X-ray diffraction, the product was found to be unconverted P-
BN powder, hBN powder or hBN powder and a trace amount of C
It was a mixture with BN powder.

(Effects of the Invention) According to the present invention, CBN can be manufactured under high temperature and high pressure treatment conditions with excellent productivity. CBN produced according to the present invention can be extremely effectively used as a heat sink for electronic devices or as a tool for machining difficult-to-cut materials.

Claims (1)

[Claims] 1. In producing cubic boron nitride by treating pyrolytic boron nitride at high temperature and high pressure without using a catalyst, the pyrolytic boron nitride is precipitated from a gas phase. In the state as it is, it has a structure in which hexagonal scale-like hexagonal boron nitride particles are randomly oriented, and the interlayer distance in the c-axis direction (d00
2) is 3.35 Å or less, and the density is 2.18 g/cm
larger than ^3, and the crystallite size in the c-axis direction is 1000
Å or more, and the purity is 99.995% or more,
A method for producing cubic boron nitride, characterized in that the high temperature and high pressure conditions are a temperature of 1500° C. or higher and a pressure of 50,000 atmospheres or higher.